Catalytic system, its method for preparation and method for preparation of a copolymer of ethylene and a conjugated diene

ABSTRACT

The present invention provides to a catalytic system, its method for preparation, and a method for preparation of a copolymer of ethylene and a conjugated diene, which uses this catalytic system. A catalytic system according to the invention comprises: 
     an organometallic complex compound, which is represented by one formula A or B:                    
     in which Ln represents a metal of a lanthanide, the atomic number of which is between 57 and 71; 
     X represents a halogen, which can be chlorine, fluorine, bromine or iodine; and 
     Cp 1  and Cp 2  each comprise a cyclopentadienyl or fluorenyl group, which is or is not substituted, and 
     P is a bridge corresponding to the formula MR 2 , in which M is an element of column IVA of Mendeleev&#39;s periodic classification, and R is an alkyl group comprising from 1 to 20 atoms of carbon; and 
     a co-catalyst selected from among a magnesium alkyl, a lithium alkyl, an aluminium alkyl, or a Grignard&#39;s reagent, and mixtures thereof.

CROSS REFERENCE TO RELATED APPLICATION(S)

This application is a divisional of U.S. patent application Ser. No. 09/689,464, filed Oct. 12, 2000 now U.S. Pat. No. 6,569,799, which claims priority to French Application No. 99/12798, filed Oct. 12, 1999.

BACKGROUND OF THE INVENTION

The present invention relates to a catalytic system which can be used for copolymerization of ethylene and a conjugated diene monomer, a method for preparation of this catalytic system, and a method for preparation of a copolymer of ethylene and a conjugated diene monomer, using the catalytic system.

It is known that ethylene may be polymerized using certain complex compounds based on lanthanide. These catalysts can be used over a wide range of pressures and temperatures, advantageously at a reduced pressure and a temperature which is close to ambient temperature, for the polymerization of ethylene.

The first complex compounds based on lanthanide described in the literature were alkylated complex compounds. In particular, in J. Chem. Soc., Chem. Comm. pp 994-995 (1978), Ballard et al. described the polymerization of ethylene by means of a complex compound corresponding to the formula [(C₅H₅)₂ErMe]₂ (in which Me is a methyl group).

These alkylated complex compounds can achieve instantaneous levels of activity which are very high, as described in U.S. Pat. No. 4,716,257, with reference to a similar complex compound corresponding to the formula [(C₅Me₅)₂LnH]₂ (in which Ln represents a lanthanide).

However, a major disadvantage of these alkylated complex compounds is that they are deactivated very quickly. Another disadvantage consists in the relative complexity of their synthesis.

In order to eliminate these disadvantages, there have been attempts to develop non-alkylated complex compounds which are based on lanthanide. These complex compounds have a metal-halogen bond and are alkylated in the polymerization medium. U.S. Pat. No. 5,109,085 describes the polymerization of ethylene with complex compounds having the formula C_(Pn)LnX_(4-n)M′Lx (in which L is a complexing molecule, and x is a whole number equivalent to, or higher than 1), which have one or more co-catalysts added to them. The patent also refers to the possible use of the complex for copolymerizing ethylene and butadiene.

This type of non-alkylated complex compound has in its environment one or more complexing molecules L, which for example can consist of tetrahydrofurane or diethylic ether, and are added for reasons of organometallic synthesis.

However, it is found that these complexing molecules can compete with the ethylenic monomer during complexing on the lanthanide, with the undesirable consequence of limiting catalytic activity and, thus, the polymerization output.

In addition, Cui, Li Qiang et al: “Preliminary investigations on polymerization catalysts composed of lanthanocene and methyl aluminoxane”, Polymer Bulletin (Berlin), 1998, 40(6), pp 729-734, describe a catalytic system which is designed for homopolymerization of isoprene, butadiene, or styrene. This catalytic system comprises:

a rare earth organometallic complex compound in accordance with one or another of the following formula:

(C₅H₉Cp)₂NdCl  (I);

(C₅H₉Cp)₂SmCl  (II);

(MeCp)₂SmOAr′  (III);

(Ind)₂NdCl  (IV);

Me₂Si(Ind)₂NdCl  (V);

(Flu)₂NdCl  (VI);

 in which Cp, Ind and Flu are respectively cyclopentadienyl, indenyl and fluorenyl groups, and OAr′ is a phenoxy group; and

a co-catalyst consisting of methylaluminoxane, tested in comparison with a co-catalyst consisting of an aluminium alkyl.

The present invention provides an improved catalytic system for preparing copolymers of ethylene and a conjugated diene which do not have the aforementioned disadvantages of the art.

SUMMARY OF THE INVENTION

The present invention provides a catalytic system for copolymerizing ethylene and a conjugated diene comprising an organometallic complex compound represented by one of the following generic formula A′ or B′:

in which Ln represents a metal of a lanthanide, the atomic number of which is between 57 and 71;

X represents a halogen, selected from among chlorine, fluorine, bromine and iodine; wherein

in formula A′, two ligand molecules Cp₁ and Cp₂, which may be identical or different, selected from a substituted or unsubstituted cyclopentadienyl and fluorenyl group are bonded to metal Ln; and

in formula B′, a ligand comprising Cp₁ and Cp₂ bonded to each other by a bridge P is bonded to metal Ln, wherein Cp₁ and Cp₂ comprise a substituted or unsubstituted cyclopentadienyl or fluorenyl group, bridge P corresponds to the formula MR₂, in which M is silicon or another element of column IVA of Mendeleev's periodic classification and R is an alkyl group having 1 to 20 atoms of carbon;

and a co-catalyst selected from the group consisting of a magnesium alkyl, a lithium alkyl, an aluminum alkyl, a Grignard's reagent and mixtures thereof.

In a preferred embodiment metal, Ln is neodymium. Cp₁ and Cp₂ are preferably identical, each being a cyclopentadienyl group. More preferably, Cp₁ and Cp₂ are each a cyclopentadienyl group, substituted by an alkyl radical or a silyl alkyl radical.

The invention also provides for methods for preparing the catalytic system and its use thereof in preparing copolymers of ethylene and a conjugated diene.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides an improved catalytic system for preparing copolymers of ethylene and a conjugated diene which do not have the aforementioned disadvantages of the art. The present invention provides a catalytic system for copolymerizing ethylene and a conjugated diene comprising an organometallic complex compound represented by one of the following generic formula A′ or B′:

in which Ln represents a metal of a lanthanide, the atomic number of which can be between 57 and 71;

X represents a halogen, selected from among chlorine, fluorine, bromine and iodine; wherein

in formula A′, two ligand molecules Cp₁ and Cp₂, which may be identical or different, selected from a substituted or unsubstituted cyclopentadienyl and fluorenyl group are bonded to metal Ln; and

in formula B′, a ligand comprising Cp₁ and Cp₂ bonded to each other by a bridge P, is bonded to metal Ln, wherein Cp₁ and Cp₂ comprise a substituted or unsubstituted cyclopentadienyl or fluorenyl group, bridge P corresponds to the formula MR₂, in which M is silicon or another element of column IVA of Mendeleev's periodic classification and R is an alkyl group having 1 to 20 atoms of carbon;

and a co-catalyst selected from the group consisting of a magnesium alkyl, a lithium alkyl, an aluminum alkyl, a Grignard's reagent and mixtures thereof.

In a preferred embodiment, Ln is neodymium. Cp₁ and Cp₂ are preferably identical, each being a cyclopentadienyl group. More preferably, Cp₁ and Cp₂ are each a cyclopentadienyl group, substituted by an alkyl radical or a silyl alkyl radical.

Thus, in one aspect, the catalytic system of the invention comprises an organometallic complex compound, which is represented by one of formula A′ or B′:

in which Ln represents a metal of a lanthanide, the atomic number of which is between 57and 71;

X represents a halogen selected from among chlorine, fluorine, bromine and iodine; wherein

in formula A, two ligand molecules CP_(A), each a substituted cyclopentadienyl group, are bonded to metal Ln;

and in formula B, a ligand, comprising two Cp_(B), bonded to one another by a bridge P are bonded to metal Ln, wherein Cp_(B) is a substituted or unsubstituted cyclopentadienyl or fluorenyl group and P corresponds to formula MR₂, in which M is an element in column IVA of Mendeleev's periodic classification, and R is an alkyl group having 1 to 20 carbon atoms; and

a co-catalyst selected from the group consisting of a magnesium alkyl, a lithium alkyl, an aluminium alkyl, a Grignard's reagent, and mixtures thereof.

In the case of substitution by a silyl alkyl radical, Cp₁ and Cp₂ each correspond to formula CP_(A)═(C₅H₄)(SiMe₃) in generic formula A′, or to formula Cp_(B)═(C₅H₃)(SiMe₃) in generic formula B′, where Me represents a methyl group. The organometallic complex compound then corresponds to particular formula A or B hereinafter, as applicable.

In particular formula A, two molecules of CP_(A), each of which corresponds to formula (C₅H₄)(SiMe₃) are bonded to metal Ln, and in particular formula B, a ligand molecule, comprising two molecules of Cp_(B), each a substituted cyclopentadienyl group corresponding to the formula (C₅H₃)(SiMe₃), bonded to each other by bridge P, is bonded to metal Ln.

In a further embodiment, Cp₁ and Cp₂ are identical, each comprising a non-substituted fluorenyl group which corresponds to formula C₁₃H₉, in generic formula A′, or which corresponds to the formula C₁₃H₈, for the said generic formula B′. In the latter case, there corresponds to the formula B′ the aforementioned particular formula B, in which Cp_(B)═C₁₃H₈.

If Cp₁═Cp₂═Cp, said organometallic complex compound is prepared as follows:

(a) preparing a hydrogenated molecule of ligand, represented by the formula HCp, which is reacted with a lithium alkyl to obtain a lithium salt;

(b) reacting the lithium salt in a complexing solvent with an anhydrous lanthanide trihalide, represented by formula LnX₃, where X represents a halogen selected from among chlorine, fluorine, bromine and iodine to produce a reaction product;

(c) evaporating the complexing solvent, and extracting in a non-complexing solvent the reaction product of (b) to produce an extracted reaction product; and, optionally:

(d) crystallizing the extracted reaction product of (c), in order to obtain the organometallic complex compound which corresponds to formula A or B, which are completely free from the complexing solvent.

In step (a), lithium butyl is the preferred lithium alkyl.

In step (b), tetrahydrofurane (THF) is the preferred complexing solvent. In addition, two moles of the lithium salt are advantageously reacted with one or two moles of the lanthanide trihalide.

Toluene or heptane are preferred non-complexing solvents in step (c).

When the co-catalyst is a mixture of an aluminium alkyl and a lithium alkyl, these two components are advantageously present in quantities which are stoichiometric, or close to the stoichiometry in the mixture, in order to obtain satisfactory catalytic activity.

Preferred co-catalysts include magnesium butyloctyl, lithium butyl, aluminium diisobutyl hydride, magnesium butyl chloride and mixtures thereof.

In accordance with the invention, copolymers of ethylene and a conjugated diene are prepared by reacting the catalytic system comprising the organometallic complex compound and the co-catalyst with ethylene and a conjugated diene monomer in an inert hydrocarbon solvent.

Suitable conjugated dienes include 1,3-butadiene, 2-methyl 1,3-butadiene (hereinafter referred to as butadiene and isoprene, respectively), 2,3-di(C1 to C5 alkyl) 1,3-butadienes, such as 2,3 dimethyl-1,3 butadiene, 2,3-diethyl-1,3-butadiene, 2-methyl 3-ethyl 1,3-butadiene, 2-methyl 3-isopropyl 1,3-butadiene, phenyl 1,3-butadiene, 1,3-pentadiene, 2,4-hexadiene, and any other conjugated diene having has between 4 and 8 carbon atoms.

The polymerization reaction can be carried out in suspension or in solution, at a variable pressure, and at a temperature of between −20° C. and 220° C., preferably between 20° C. 90° C.

The molar ratio of co-catalyst to organometallic complex compound is 1 or more, preferably 2 to 100.

The concentration of lanthanide in the reaction medium is advantageously lower than 0.3 mmole/l.

The molar fraction of butadiene in the reaction medium is advantageously between 1% and 80%.

With reference to Appendix I below, the copolymer of ethylene and a conjugated diene produced by the method of the invention can have the following microstructure characteristics, according to the organometallic complex compound used for the catalytic system.

If butadiene is the conjugated diene, the copolymer obtained can have the following chain formations for the butadiene units inserted in the copolymer: 1,4 cis; 1,4 trans; 1,2, or it can be in the form of trans 1,2 cyclohexane. (See Appendix I).

More particularly, when the organometallic complex compound corresponds to one of formulae [(C₅H₄)SiMe₃]₂NdCl, {[(C₅H₃)SiMe₃]SiMe₂}NdCl or (C₁₃H₉)₂NdCl, most of the butadiene in the copolymer will comprise 1,4 trans chain formations.

When the complex compound corresponds to the formula [(C₁₃H₈)₂SiMe₂]NdCl, most of the butadiene in the copolymer chain will have a 1,2 trans cyclohexane configuration.

If isoprene is the conjugated diene, the copolymer obtained can have the following chain formations for the isoprene units inserted in the copolymer: 1,4; 1,2 or 3,4.

More particularly, when the organometallic complex compound corresponds to formula [(C₅H₄)SiMe₃]₂NdCl, most of the isoprene is inserted in the copolymer chain by 1,4 bonds chain formations.

When the complex compound corresponds to formula [(C₁₃H₈)₂SiMe₂]NdCl, most of the isoprene inserted in the copolymer by 3,4 chain formations.

A further characteristic of the ethylene and butadiene copolymers obtained by the method of the invention, is that they have an “ethylene-butadiene” chain formation statistic which is substantially of the alternating type, when the organometallic complex compound corresponds to formula [(C₅H₄)SiMe₃]₂NdCl or formula {[C₅H₃)SiMe₃]₂SiMe₂}NdCl, and a chain formation statistic that is substantially of the block type, when the complex compound corresponds to formula (C₁₃H₉)₂NdCl. (See Appendix II below).

The aforementioned characteristics of the present invention, as well as others, will be better understood in view of the above description and the following non-limiting Examples 1-4 of embodiments of the invention compared to Example 5, which illustrates the prior state of the art.

For all of the following examples, the work was carried out using argon, and the solvents used were previously dried by distillation or on a 3 Å molecular sieve swept with argon.

The microstructure of the copolymers obtained in the examples was determined first by of RMN¹H techniques, and second by the RMN¹³C technique. For this purpose, a spectrometer sold under the name “BRUKER” was used, at frequencies of 400 MHz for the RMN¹H technique, and 100.6 MHz for the RMN¹³C technique.

Appendix I describes the method for determining of this microstructure.

Appendix II describes the method for determining “ethylene-butadiene” chain formation statistic.

EXAMPLE 1 Catalytic System Comprising a Neutral, Non-bridged Organometallic Complex Compound: chloro bis(η5-trimethylsilylcyclopentadienyl)neodymium, Corresponding to Formula [(C₅H₄)SiMe₃]₂NdCl (Generic Formula A′)

Synthesis of a Salt Having the Formula Li[(C₅H₄ SiMe₃]

A compound of formula (C₅H₅)SiMe₃ and 80 ml of dry heptane are introduced into a 20 mmole Schlenk tube. 20 mmoles of lithium butyl is then added gradually at ambient temperature. The solution obtained is agitated for three hours at ambient temperature until the emission of gas ceases. A white precipitate is obtained, which is filtered and washed twice with 40 ml of heptane. It is then dried under vacuum, in order to obtain the salt.

Synthesis of the Organometallic Complex Compound Having Formula [(C₅H₄)SiMe₃]₂NdCl

Reflux agitation is carried out overnight of a solution of 4 mmoles of anhydrous NdCl₃ in tetrahydrofurane (THF). 8 mmoles of the salt having formula Li[(C₅H₄)SiMe₃] is then added to this solution. Reflux agitation is then carried out on the mixture obtained in THF for 48 hours, followed by evaporation of the THF. Then 60 ml of toluene are added to the mixture. The salt present in solution is filtered, the remaining solution is concentrated, and is then crystallized at −30° C. to provide the organometallic complex compound.

Elementary centesimal analysis of this complex compound provides the following percentages for the carbon and hydrogen atoms:

% C=42.05 and % H=5.9.

The resulting organometallic complex compound was characterized by means of the RMN¹H technique at 300 MHz.

By means of this technique, two masses can be observed, each integral of which corresponds to 4 protons, i.e.:

a first mass with 26.55 ppm is representative of the protons of C₅H₄ which are bonded to the first cyclopentadienyl group of this complex compound, and a second mass with 11.4 ppm is representative of the C₅H₄ protons which are bonded to the second cyclopentadienyl group.

Finally, a mass is observed with −12.38 ppm, the integral of which corresponds to 18 protons, which is representative of the protons of the two substituents Si(CH₃)₃ of the complex.

Method for Copolymerization of Ethylene and Butadiene

Four tests are carried out, each of which corresponds to a single introduction into a reactor containing approximately 300 ml of toluene, of a pre-determined quantity x (mg) of the organometallic complex compound having formula [(C₅H₄)SiMe₃]₂NdCl, a mixture of ethylene and butadiene with a pre-determined molar fraction y (%) of butadiene, and a co-catalyst. The temperature in the reactor is raised to 80° C.

When the fraction y of butadiene permits it, the pressure inside the reactor is maintained at a constant value, equivalent to 4 bars.

After a time t, the polymerization is halted by cooling and de-gassing of the reactor, thereafter the polymer obtained is precipitated in methanol. After drying has been carried out, a mass m of polymer is obtained.

For each of the first three tests, the co-catalyst comprises a mixture of lithium butyl and aluminium diisobutyl hydride (hereinafter, BuLi and HDiBA, respectively), in the following molar proportions:

BuLi/HDiBA/neodymium=10/10/1.

For the fourth test, the co-catalyst comprises magnesium butyloctyl (hereinafter BOMAG), in a molar proportion of 20/1 relative to neodymium.

Table I below shows the operative conditions and the results obtained for the above-described four tests.

TABLE I stereochemistry of insertion of the butadiene in the y (%) in copolymer x monomer % butadiene in % 1, 4 % trans 1, 2 t m tests (mg) mixture the copolymer % 1, 2 trans cyclohexane co-catalyst (min) (g) n°1 29 0 0 — — — BuLi + HDiBA 30 20 n°2 32 3.9 3.5 4 96 0 BuLi + HDiBA 80 3.7 n°3 36 21.2 16.4 3 97 0 BuLi + HDiBA 260 2 n°4 16 4.5 9.5 8.6 85.2 6.2 BOMAG 132 1.2

The “ethylene-butadiene” chain formation statistic for the copolymer obtained in test no. 3 was determined.

Using the method set forth below in Appendix II, the following was obtained for this copolymer:

a block index η equivalent to 1.12; and

a block index η_(alternating) (corresponding to a perfectly alternating copolymer with the same composition) equivalent to 1.19.

It can be deduced that this copolymer has a tendency towards alternance for these chain formations.

Method for Copolymerization of Ethylene and Isoprene

The organometallic complex compound having formula [(C₅H₄)SiMe₃]₂NdCl synthesized as above is used.

Three tests are carried out, each of which corresponds to introduction into a reactor of a solution comprising 300 ml of toluene, x (mg) complex compound of formula [(C₅H₄)SiMe₃]₂NdCl, BuLi, HDiBA and y (ml) of isoprene.

BuLi and HDiBA are introduced in molar ratio to neodymium as follows:

BuLi/neodymium=10 and HDiBA/neodymium=10.

The temperature inside the reactor is raised to 80° C., and ethylene is added to the solution. The pressure inside the reactor is maintained constant, equivalent to 4 bars.

After a time t, the polymerization is halted by cooling and de-gassing of the reactor, then the resulting copolymer is precipitated in methanol.

Table II below shows the operative conditions and the results obtained for the above-described three tests.

TABLE II stereochemistry of insertion of the isoprene in the x y % isoprene in copolymer t m tests (mg) (ml) the copolymer % 1, 2 % 1, 4 % 3, 4 co-catalyst (min) (g) n°1 49.5 1 0.98 2.3 89.7 8.0 BuLi + HdiBA 60 3.37 n°2 48.2 3 0.96 2.3 89.6 8.1 BuLi + HdiBA 60 2.42 n°3 45.2 10 3.8 1.6 90.9 7.5  BuLi + HDiBA 60 1.29

EXAMPLE 2 Catalytic System Comprising a Neutral, Bridged Organometallic Complex Compound: chloro(μ-dimethylsilyl)bis(η5-trimethylsilylcyclopentadienyl)neodymium, Corresponding to Formula {[(C₅H₃)SiMe₃]₂SiMe₂}NdCl (Generic Formula B′)

Synthesis of a Compound Having Formula [(C₅H₄)SiMe₃]₂SiMe₂

16 mmoles of a compound of formula Li[(C₅H₄)SiMe₃], 8 mmoles of Me₂SiCl₂ and 80 ml of THF are introduced into a Schlenk tube. The mixture is agitated together overnight at ambient temperature. Part of the THF is then evaporated, and heptane is added. In succession, the solution obtained is then hydrolyzed, washed with an aqueous solution saturated with NH₄Cl, and dried on magnesium sulphate. The THF is then evaporated, and the product finally obtained is a viscous oil which corresponds to the aforementioned formula.

Synthesis of a Salt Having Formula [(C₅H₃)SiMe₃]₂SiMe₂Li₂

14 mmole of BuLi is added gradually at 0° into a Schlenk tube which contains a solution of THF comprising 7 mmoles of the compound formula [(C₅H₄)SiMe₃]₂SiMe₂. The mixture is agitated together at ambient temperature for 6 hours, then the product obtained is precipitated by addition of heptane. The precipitate is then filtered, washed with heptane, and dried under vacuum to obtain the salt.

Synthesis of the Organometallic Complex Compound Having Formula {[C₅H₃)SiMe₃]₂SiMe₂}NdCl

Reflux agitation is carried out overnight on 4 mmoles of anhydrous NdCl₃ in THF. 4 mmoles of the salt of formula [(C₅H₃)SiMe₃]₂SiMe₂Li₂ is then added to this suspension. The mixture is then agitated, in a first stage for 4 hours at ambient temperature, then in a second stage for 24 hours with reflux in THF. The THF is evaporated, and toluene is added. The salt is filtered, then the product finally obtained after having been concentrated is crystallized at a temperature of −10° C. to obtain the organometallic complex compound.

Elementary centesimal analysis of this complex compound gives the following percentages for the atoms of carbon and hydrogen:

% C=42.8 and % H=5.75.

This organometallic complex compound was characterized by means of the RMN¹H technique at 300 MHz. By means of this technique, two masses can be observed, each integral of which corresponds to 3 protons, i.e.:

a first mass with 2.13 ppm and a second mass with −8.97 ppm are each representative of the protons of Si(CH₃)₂ in this complex compound.

Finally, a mass with −2.99 ppm is observed, the integral of which corresponds to 18 protons, which is representative of the protons in the two substituents Si(CH₃)₃ of the complex compound.

It will be noted that the peaks corresponding to the protons of C₅H₃ are not detected, probably owing to the fact that these peaks are very wide.

Method for Copolymerization

Three tests are carried out following the procedure of Example 1, with the difference being that the compound having the formula {[(C₅H₃)SiMe₃]₂SiMe₂}NdCl is used as the organometallic complex compound.

For each of these three tests, the co-catalyst comprises a mixture of BuLi and HDiBA, in accordance with the following molar proportions:

BuLi/HDiBA/neodymium=10/10/1.

Table III below shows the operative conditions and the results obtained for the above-described three tests.

TABLE III stereochemistry of insertion of the butadiene in the y (%) in copolymer x monomer % butadiene in % 1, 4 % trans 1, 2 t m tests (mg) mixture the copolymer % 1, 2 trans cyclohexane co-catalyst (min) (g) n°1 31 5.4 6.9 2 98 0 BuLi + HDiBA  30 13.5 n°2 30 43 41 2.5 97.5 0 BuLi + HDiBA 120 4.8 n°3 36 80 61.5 4.5 95.5 0 BuLi + HDiBA 900 0.5

The “ethylene-butadiene” chain formation statistic for the copolymer obtained in test no. 2 was determined.

Using the method set forth in Appendix II, the following was obtained for this copolymer:

a block index η equivalent to 1.69; and

a block index η_(alternating) (corresponding to a perfectly alternating copolymer with the same composition) equivalent to 1.78.

It can be deduced that this copolymer has a tendency towards alternance for these chain formations.

EXAMPLE 3 Catalytic System Comprising a Neutral, Non-bridged Organometallic Complex Compound: chloro bis(η5-fluorenyl)neodymium, Corresponding to the Formula (C₁₃H₉)₂NdCl (Generic Formula A′)

Synthesis of a Salt Having Formula C₁₃H₉Li

Thirty-nine (39) mmoles of a compound of formula C₁₃H₁₀ is reacted with 39 mmoles of BuLi overnight, then for 3 hours with reflux in heptane at ambient temperature. The salt obtained is washed with heptane, then is dried under vacuum to obtain the identified salt.

Synthesis of the Organometallic Complex Compound Having Formula (C₁₃H₉)₂NdCl

1.6 mmoles of NdCl₃ in THF is agitated and refluxed. The suspension obtained is cooled to ambient temperature, then 3.25 mmole of the salt of formula C₁₃H₉Li is added. The mixture is agitated overnight at ambient temperature, then refluxed for 4 hours. After the THF has been evaporated, the product obtained is extracted with toluene, and recuperated from the toluene by evaporation under vacuum to obtain the organometallic complex compound.

Method for Copolymerization

Four tests are carried out following the procedure in Example 1, with the only difference being that the compound having formula (C₁₃H₉)₂NdCl is used as the organometallic complex compound.

For the first three tests, the co-catalyst comprises a mixture of BuLi and HDiBA, in the following molar proportions:

BuLi/HDiBA/neodymium=10/10/1.

For the fourth test, the co-catalyst comprises magnesium butyloctyl, in a molar proportion of 20/1 relative to the neodymium.

Table IV below shows the operative conditions and the results obtained for the above-described four tests.

TABLE IV stereochemistry of insertion of the butadiene in the y (%) in copolymer x monomer % butadiene in % 1, 4 % 1, 4 % trans 1, 2 t m tests (mg) mixture the copolymer % 1, 2 trans cis cyclohexane co-catalyst (min) (g) n°1 24.9 4 3.6 8 82 0 10 BuLi + HDiBA 65 2.7 n°2 24.5 20 9.2 9 79-83 0 12-7 BuLi + HDiBA 120 1.7 n°3 26 30 42 13 75 9 3 BuLi + HDiBA 1560 0.8 n°4 24.4 4.5 4 6 87.5 0 6.5 BOMAG 100 1.2

The “ethylene-butadiene” chain formation statistic for the copolymer obtained in test no. 3 was obtained.

Using the method in Appendix II, the following was obtained for this copolymer:

a block index η equivalent to 0.4; and

a block index η_(alternating) (corresponding to a perfectly alternating copolymer with the same composition) equivalent to 1.7.

It can be deduced that this copolymer has a tendency towards alternance for these chain formations.

EXAMPLE 4 Catalytic System Comprising a Bridged Neutral Organometallic Complex Compound: chloro(μ-dimethylsilyl)bis(η5-fluorenyl)neodymium, Corresponding to the Formula [(C₁₃H₈)₂SiMe₂]NdCl (Generic Formula B′)

Synthesis of a Compound Having Formula Me₂Si(C₁₃H₉)₂

Reflux agitation of 18 mmoles of C₁₃H₁₀ and 18 mmoles of sodium hydride is carried out overnight in THF. 8.1 mMoles of Cl₂SiMe₂ is then added to this mixture, then the solution obtained is agitated for 3 hours at ambient temperature. Following evaporation of some of the THF, heptane is added. The organic phase obtained is hydrolyzed and extracted several times by an aqueous solution saturated with NH₄Cl. The solvent is then evaporated and, after the extract has been dried under vacuum at 60° C., the compound corresponding to the above formula is obtained.

Synthesis of a Salt Having Formula Me₂Si(C₁₃H₈)₂Li₂

4.4 mmoles of the compound of formula Me₂Si(C₁₃H₉)₂ and 13 mmoles of BuLi are agitated overnight at ambient temperature in toluene, and then for 3 hours at 50° C. A precipitate is obtained comprising a salt which corresponds to the above formula, which is washed with heptane, then dried under vacuum.

Synthesis of the Organometallic Complex Compound Having Formula [(C₁₃H₈)₂SiMe₂]NdCl]

2 mmoles of NdCl₃ is agitated with reflux overnight in THF. 2.1 moles of the salt are added at 0° C., then the mixture is heated with reflux for 22 hours. The THF is then evaporated, and the organometallic complex compound is recuperated by extraction with toluene, followed by evaporation of the latter.

Method for Copolymerization of the Ethylene and Butadiene

Five tests are carried out in accordance with Example 1, with the difference being that the compound having formula [(C₁₃H₈)SiMe₂]NdCl is used as the organometallic complex compound.

For the first two tests, the co-catalyst comprises a mixture of BuLi and HDiBA, in the following molar proportions:

BuLi/HDiBA/neodymium=10/10/1.

For the third and fourth tests, the co-catalyst comprises magnesium butyl chloride, in a molar proportion of 20/1 relative to the neodymium.

For the fifth test, the co-catalyst comprises of BuLi, in a molar proportion of 2/1 relative to the neodymium.

Table V below shows the operative conditions and the results obtained for the above-described five tests.

TABLE V stereochemistry of insertion of the butadiene in the y (%) in copolymer x monomer % butadiene in % 1, 4 % trans 1, 2 t m tests (mg) mixture the copolymer % 1, 2 trans cyclohexane co-catalyst (min) (g) n°1 21.3 5 4 18 23 58 BuLi + HDiBA 70 9.9 n°2 25.8 20 10.2 23.5 28.5 48 BuLi + HDiBA 135 3 n°3 18.9 5 3.9 20 18 62 butyl MgCl 65 12.1 n°4 17.3 19 21 28 22 50 butyl MgCl 60 2.8 n°5 19.2 4.5 5.4 23 23 54 BuLi 60 3.7

Method for Copolymerization of Ethylene and Isoprene

The organometallic complex compound having formula [(C₁₃H₈)₂SiMe₂]NdCl as synthesized above is used.

A test is carried out following the method of Example 1.

Table VI below shows the operative conditions and the results obtained for this test.

TABLE VI stereochemistry of insertion of the isoprene in the x y % isoprene in copolymer t m (mg) (ml) the copolymer % 1, 2 % 1, 4 % 3, 4 co-catalyst (min) (g) 31.1 1 2.12 1.6 21.5 76.9 BuLi + HDiBA 6 4.30

EXAMPLE 5 Catalytic System Comprising a Known Organometallic Complex Compound, Corresponding to the Formula (C₅Me₅)₂NdCl₂Li(OEt₂)₂.

Synthesis of a Salt Having Formula Li(C₅Me₅)

29.9 mmoles of BuLi is added to 29.9 mmoles of HC₅Me₅ in heptane at 0° C. The mixture is agitated at ambient temperature overnight. The salt Li(C₅Me₅) thus obtained is then washed, then dried under vacuum.

Synthesis of an Organometallic Complex Compound with the Formula (C₅Me₅)₂NdCl₂Li(OEt₂)₂

9.2 mmoles of neodymium trichloride NdCl₃ is agitated with reflux overnight in tetrahydrofurane (THF). The suspension thus obtained is lowered to 0° C., then 18.4 mmoles of the salt of formula Li(C₅Me₅) is added. The mixture is agitated overnight with reflux. The THF is then evaporated, then ether is added to the solution obtained. The resulting solution is filtered, then concentrated. Finally, the organometallic complex compound corresponding to the above formula is obtained by crystallization at −30° C.

Method for Copolymerization of Ethylene and Butadiene

Two tests are carried out following the procedure in Example 1, with the difference being that the compound having formula (C₅Me₅)₂NdCl₂Li(OEt₂)₂ is used as the organometallic complex compound.

Table VII below shows the operative conditions and the results obtained with the aforementioned mixture of BuLi and HDiBA as co-catalyst, in molar proportions of lithium butyl/HDiBA/neodymium equivalent to 10/10/1.

TABLE VII stereochemistry of insertion of the butadiene in the y in copolymer x monomer % butadiene in % 1, 4 % trans 1, 2 t m tests (mg) mixture the copolymer % 1, 2 trans cyclohexane co-catalyst (min) (g) n°1 18.7 5 0.6 30 70 0 BuLi + HDiBA 65 1.6 n°2 14.4 5 0.6 76 24 0 BuLi + HDiBA 60 1.4 

We claim:
 1. A method for preparing a copolymer of ethylene and a conjugated diene, comprising reacting a catalytic system with ethylene and a conjugated diene monomer in an inert hydrocarbon solvent, wherein the catalytic system comprises: an organometallic complex compound, which is represented by one of formula A′ or B′:

in which Ln represents a metal of a lanthanide, the atomic number of which is between 57 and 71; X represents a halogen, selected from the group consisting of chlorine, fluorine, bromine and iodine; wherein in formula A′, two ligand molecules Cp₁ and Cp₂, which may be identical or different, selected from a substituted or unsubstituted cyclopentadienyl or fluorenyl group, are bonded to metal Ln; and in formula B′, a ligand comprising Cp₁ and Cp₂ bonded to each other by a bridge P is bonded to metal Ln, wherein Cp₁ and Cp₂ comprise a substituted or unsubstituted cyclopentadienyl or fluorenyl group, wherein P corresponds to formula MR₂, in which M is an element in column IVA of Mendeleev's periodic classification, and R is an alkyl group having 1 to 20 carbon atoms; and a co-catalyst selected from the group consisting of a magnesium alkyl, a lithium alkyl, an aluminium alkyl, a Grignard's reagent, and mixtures thereof.
 2. The method for preparation of a copolymer of ethylene and a conjugated diene according to claim 1, wherein the organometallic complex compound is represented by formula A′:


3. The method for preparation of a copolymer of ethylene and a conjugated diene according to claim 1, wherein the organometallic complex compound is represented by formula B′:


4. The method for preparation of a copolymer of ethylene and a conjugated diene according to claim 3, wherein the metal M of bridge P is silicon.
 5. The method for preparation of a copolymer of ethylene and a conjugated diene according to claim 1, wherein metal Ln is neodymium.
 6. The method for preparation of a copolymer of ethylene and a conjugated diene according to claim 1, wherein Cp₁ and Cp₂ are identical, each being a cyclopentadienyl group.
 7. The method for preparation of a copolymer of ethylene and a conjugated diene according to claim 6, wherein the Cp₁ and Cp₂ are each a cyclopentadienyl group substituted by an alkyl radical or silyl alkyl.
 8. The method for preparation of a copolymer of ethylene and a conjugated diene according to claim 2, wherein Cp₁ and Cp₂ each correspond to formula (C₅H₄)(SiMe₃), in which Me represents a methyl group.
 9. The method for preparation of a copolymer of ethylene and a conjugated diene according to claim 3, wherein Cp₁ and Cp₂ each correspond to formula (C₅H₃)(SiMe₃), in which Me represents a methyl group.
 10. The method for preparation of a copolymer of ethylene and a conjugated diene according to claim 1, 2 or 3, wherein Cp₁ and Cp₂ are identical, each being a fluorenyl group.
 11. The method for preparation of a copolymer of ethylene and a conjugated diene according to claim 2, wherein Cp₁ and Cp₂ are each a non-substituted fluorenyl group which corresponds to formula C₁₃H₉.
 12. The method for preparation of a copolymer of ethylene and a conjugated diene according to claim 3, wherein Cp₁ and Cp₂ are each a non-substituted fluorenyl group which corresponds to formula C₁ ₃H₈.
 13. The method for preparation of a copolymer of ethylene and a conjugated diene according to claim 1, wherein the co-catalyst is selected from the group consisting of magnesium butyloctyl, lithium butyl, aluminium diisobutyl hydride, and magnesium butyl chloride and mixtures thereof.
 14. The method for preparation of a copolymer of ethylene and a conjugated diene according to claim 1, wherein the co-catalyst comprises a mixture of an aluminium alkyl and a lithium alkyl, which are present in substantially stoichiometric quantities in the mixture.
 15. The method for preparation of a copolymer of ethylene and a conjugated diene according to claim 1 further comprising reacting the catalytic system with the ethylene and conjugated butadiene monomer in suspension or in solution, at a temperature of between 20° C. and 90° C.
 16. The method for preparation of a copolymer of ethylene and a conjugated diene according to claim 1, wherein the molar ratio of the co-catalyst to the organometallic complex compound is between 2 and
 100. 17. The method for preparation of a copolymer of ethylene and a conjugated diene according to claim 1, wherein the concentration of metal Ln in the reactive medium is less than 0.3 mmole/l.
 18. The method for preparation of a copolymer of ethylene and a conjugated diene according to claim 1, wherein the molar fraction of conjugated diene in the copolymer is between 1% and 80%.
 19. The method for preparation of a copolymer of ethylene and a conjugated diene according to claim 1, wherein the conjugated diene co-monomer is butadiene or isoprene. 